Total knee replacement (also known as total knee arthroplasty) surgery is a common procedure that is performed on hundreds of thousands of people each year. A number of circumstances may require replacement of a person's knee. For example, excessive deterioration of knee cartilage may necessitate knee replacement. This type of problem and other injuries to the knee may result from accidents, disease such as osteo-arthritis or rheumatoid arthritis, or other causes.
The knee joint or “knee” is formed by the bottom or distal end of the femur (or “thigh bone”) which extends from the hip, the top or proximal end of the tibia (or “shin bone”) which extends to the ankle, and the patella (or “knee cap”). The distal end of the femur and the proximal end of the tibia are covered by a smooth layer of cartilage which allows the femur and tibia to move smoothly against each other. The patella also has a smooth cartilage layer on its posterior surface to allow smooth motion against the femur. However, certain conditions, most commonly arthritis, can cause permanent deterioration of the cartilage. When the cartilage wears away, the roughened surfaces of the femur, tibia and patella may rub against each other causing pain, stiffness and swelling.
One option for treating the permanent deterioration of the cartilage is total knee replacement surgery. In a total knee replacement procedure the end surfaces of the tibia and femur, and the posterior surface of the patella, are resurfaced. Generally, the surface that covers the femoral section is made from smooth metal or ceramic, while the surface attached to the tibia is constructed of metal and a high-density polyethylene. The patella is also resurfaced with a high-density polyethylene.
The commonly known method for total knee replacement is illustrated in FIGS. 1A–1D. Illustrated in FIG. 1A is a front exterior view of a knee. The femur F, tibia T and patella P are illustrated in phantom view. In accordance with the existing total knee replacement procedure, an 8 to 12 inch incision I is made over the anterior or front portion of the knee.
Next, as illustrated in FIG. 1B, the 8–12 inch anteriorly located incision is opened exposing the patella and retinacular tissue R attached to both sides of the patella. The medial patellar retinaculum is incised, thereby allowing for the eversion of the patella P. With flexion of the knee, the patella falls posteriorly out of the way so that the interior of the knee joint is completely exposed.
Next, the distal end of the femur F, the proximal end of the tibia T, and the posterior surface of the patella are machined for acceptance of replacement knee components. In general, this step comprises affixing a cutting guide to the femur, tibia and patella, respectively, and utilizing a cutting apparatus to remove a thin layer of the arthritic surface of the femur, tibia, and patella. Further, anterior dislocation of the tibia from the femur is required to prepare the tibia. As is well known, these steps are rather exacting and requires precision if proper resection of the femur, tibia and patella is to be successful.
Knee replacement components are then connected to the tibia T and femur F as illustrated in FIG. 1C. Positioning occurs by instruments that reference external landmarks or the intramedullary canal of the femur F and tibia T. As illustrated, the components include a femoral component FC which is connected to the femur F. The femoral component FC generally has an inner surface and outer surface. The inner surface abuts the distal end of the femur F, and may include one or more elongate pegs or a box for impacting into the femur F. The femoral component is generally attached to the end of the femur using a special acrylic bone cement, or by obtaining a tight “press fit” of the femoral component FC to the femur F. The outer surface of the femoral component FC comprises one of the replacement knee surfaces.
The components also include a tibial component TC. This component has an inner surface and outer surface. The inner surface again mates to the tibia T, and as such may include a stem for impacting into the tibia T. As illustrated, the stem is somewhat long and driven into engagement by guiding the tibial component TC along the axis of the tibia T into engagement with the proximal end of the tibia T. Because of the elongated tibial stem, the tibia must be dislocated anterior to the femur for insertion of the tibial component. The tibial component TC is generally attached to the upper end of the tibia using bone cement or screws. The outer surface of the tibial component TC attaches to a high-density polyethylene insert which comprises the other of the replacement knee surfaces.
Though not illustrated, with the patella P in an everted position and exposed, the posterior of the patella P may be removed as well. A replacement patella component may be affixed to the rear of the patella P, again using bone cement.
FIG. 1D illustrates the assembled total knee replacement. As illustrated, the femoral component FC rests upon the tibial component TC. Relative motion is permitted between these two components, while at the same time protecting the femur F and tibia T. The patellar component PC glides along the femoral component with knee motion.
The existing method of total knee replacement illustrated in FIGS. 1A–1D has a number of disadvantages. One significant problem is that the procedure is quite invasive and traumatizing. The procedure results in a large incision and substantial stresses upon the body resulting in long periods of recovery/rehabilitation, and extended periods of hospitalization.
In particular, as can be seen, in order to resect the femur and tibia, and to provide sufficient access to the distal end of the femur and proximal end of the tibia, the patella must not only be moved, but everted. The patella is connected to the quadriceps tendon and muscle proximally and to the patellar ligament distally, comprising the extensor mechanism. The extensor mechanism must be stretched in order to permit the patella to be displaced and everted so as to provide frontal access to the knee. This stretching results in substantial strain and traumatization to the extensor mechanism and quadriceps muscle which takes a great deal of time to recover. In fact, in many instances a patient can not actively extend the knee for several days after the procedure. Additionally, the patellar tendon, on occasion, is ruptured or pulled loose from the tibia due to excessive strain with eversion of the patella. Also, the knee is further traumatized by displacing or dislocating the tibia anterior to the femur for tibial preparation and tibial component insertion. This strains and traumatizes the ligaments of the knee and may result in damage to the adjacent nerves and blood vessels or lead to complication including blood clots, nerve palsy, arterial injury, excessive swelling, fracture or ligament avulsion.
In addition, the size of the incision is dependent on the need to provide frontal access, including eversion of the patella, prepare the bony surface and guide the femoral, tibial and patellar components into engagement with the femur, tibia and patella along axes thereof. Use of a smaller frontal incision places excess tension on the skin, often resulting in skin necrosis or delayed healing. The large incision results in a long period of recovery and generally results in a visible scar.
An improved method and apparatus for total knee replacement is desired.